I had a new tire put on the front of my 92aspy trike it is a Michelin Pilot Activ. the old tire was the same brand. between 25 and 30 miles when slowing down I get a slight up and down bounce. never noticed it when the old tire was still on.

It could be imbalance, as well as a few other things causing the bouncing... I'd check your fork tube pressure, assuming you run air in them to see what the pressure is.. it could also be low fluid level in the fork tubes.

I am wrong as often as I am right concerning what is wrong with someone else' motorcycle without having seen the machine in person. Guessing with limited information, as to the source of the trouble, is sketchy at best.